Improvement of mechanical and dielectrical properties of ethylene propylene diene monomer (EPDM)/barium titanate (BaTiO₃) by layered mica and graphite flakes

In this study, ethylene propylene diene monomer (EPDM)/barium titanate (BaTiO₃)/mica (or graphite) composites with different volume fraction of mica (or graphite) were prepared by two-roll milling process. Thermal conductivity, crosslink density, cure, rheological, mechanical and dielectrical properties of composites were investigated. The results of rheological properties indicated that the 15 vol% mica made the complex viscosity of EPDM/BaTiO₃ compound to become non-sensitive to varying shear. In terms of mechanical properties, only 5 vol% graphite flakes remarkably improved the tensile strength of EPDM/BaTiO₃ (70/30) from 7.47 MPa to 13.20 MPa (76% increase). By comparison, the 20 vol% mica just increased the tensile strength of EPDM/BaTiO₃ (70/30) to 12.10 MPa. In addition, 20 vol% graphite flakes boosted the thermal conductivity and dielectric constant of EPDM/BaTiO₃ (70/30) from 0.323 W m⁻¹ K⁻¹ and 7.1 at 40 MHz to 2.421 W m⁻¹ K⁻¹ (749% increase) and 70 at 40 MHz (almost 1000% increase), respectively. The excellent electric and thermal performance was attributed to the mobile π electrons in graphite flakes.